Project summary The concept that sphincter of Oddi dysfunction (SOD) can cause pain and attacks of acute pancreatitis by raising bile and pancreatic duct intraductal pressure is intuitive. Each year in the U.S., thousands of patients are assigned a diagnosis of ?suspected SOD.? SOD has been considered in patients with persistent or recurrent biliary pains after undergoing cholecystectomy, and also in patients with idiopathic acute pancreatitis. The concept that SOD can cause biliary pain in patients without any objective abnormalities (a.k.a., type III SOD) was strongly contested by the EPISOD study, which irrefutably demonstrated comparable outcomes between patients who underwent sphincterotomy or sham ERCP. Following the results of the EPISOD study, the most recent consensus definition for Functional biliary sphincter of Oddi disorder (Rome IV) still relies heavily on abnormal blood chemistries and post-cholecystectomy bile duct diameter. These are the only ?objective criteria? used to distinguish patients who might still benefit from ERCP. A similar condition, functional pancreatic sphincter of Oddi disorder (FPSD), is considered for patients with idiopathic, recurrent acute pancreatitis. Given their high risk for post-ERCP pancreatitis, patients undergoing ERCP for suspected SOD are among the ideal candidates for the ongoing Stent vs. Indomethacin (SVI) trial (U01DK104833). We propose a stringent, longitudinal cohort study that is comprised of patients currently enrolled in or being considered for the parent study because of the high-risk indication of ?suspected SOD.? Unlike SVI, which terminates follow-up 30 days after randomization and ERCP, this ancillary study will follow patients for 12 months after ERCP. At the time of index ERCP, patients will undergo a systematic baseline assessment to objectively quantify their disease burden and measure potential covariates associated with response to ERCP (including pain characteristics, prior surgical history, history of emotional and physical abuse, opiate utilization, quality of life, pain-related disability, expectation of response, among others). All patients will undergo a systematic follow-up assessment at 3, 6, 9, and 12 months after their index ERCP. Using a validated tool, Patient Global Impression of Change, the primary outcome is ?improved? or ?much improved? as reported by the patient 12 months after undergoing ERCP. Additional validated instruments will be measured throughout the study period, including those developed for the Patient-Reported Outcomes Measurement Information System (PROMIS?) and a prior study of SOD (Recurrent Abdominal Pain Intensity and Disability (RAPID).